Neonatal group B streptococcal (GBS) disease is the most common disease affecting newborn infants with an estimated incidence of 1.8 per 1000 live births. Twenty-five percent of neonatal GBS disease occurs in premature infants. GBS disease results in significant mortality and morbidity in newborns. Colonization of the infant occurs via vertical transmission from a colonized mother. Among pregnant women, the rate of GBS colonization is approximately 20-30%. Approximately 42-72% of infants born to colonized mothers will become colonized, and 1-2% of these infants will develop invasive GBS disease. A major factor which may modify the rate of colonization, and possibly the risk of invasive disease is intrapartum antibiotic prophylaxis given to women who are at definably high risk for early-onset GBS disease. This intervention strategy has been shown to be near absolute in efficacy trials in conferring protection; it seems probable that substantially lower levels of protection occur when recommended regimens are attempted in routine clinical practice. Supporting this notion is data indicating that intrapartum antibiotic prophylaxis fails to prevent up to 25-30% of cases of early-onset neonatal GBS disease. The purpose of this retrospective case-control study is to evaluate the effectiveness of intrapartum antibiotic prophylaxis given to high risk women in routine clinical obstetric practice with the intent to prevent early-onset neonatal GBS disease. This objective will be accomplished by the following: 1) assembled case and control infants will comprise all live births born to high risk women at the participating hospitals over three years from January 1, 1992 through December 31, 1994; 2) cases and controls will be assembled from a retrospective review of hospital laboratory logs; and 3) perform detailed chart abstraction of clinical and demographic data from the medical records of all eligible case-control maternal and infant pairs.